1. Field of the Invention
The invention relates, in general, to ring-shaped lamp devices. In particular, the invention relates to a ring-shaped fluorescent lamp device which is used for back lighting.
2. Description of the Related Art
Straight type cold cathode and hot cathode fluorescent lamps are used as back lighting for lighting meters of an automobile, e.g., the speedometer, etc.
In recent Years, a ring-shaped fluorescent lamp has been used, instead of a straight type fluorescent lamp. The ring-shaped fluorescent lamp will light a wide area compared with the straight type fluorescent lamp. One example of a conventional fluorescent lamp used as back lighting is disclosed in Japanese Laid open patent publication 61-54150, laid open to public inspection on Mar. 18, 1986. In this prior art, various shapes of fluorescent lamps, i.e., a ring-shape, a U-shape, a rectangular-shape, and a zigzag-shape, are disclosed therein. However, such lamps are not provided with a base. It is useful to provide a base to such lamps to connect the lamp with a power supply or to mount the lamp on an external supporting device. A conventional base structure is formed in a hollow and arc shape, and is provided with a plurality of connecting pins. Such a conventional base structure may be used with a ring-shaped fluorescent lamp for back lighting. However, the conventional base structure does not rotate around the axis of the bulb of the ring-shaped fluorescent lamp to provide a prescribed clearance. Therefore, it may be difficult to adjust the position of the bulb of the lamp against the external supporting device when mounting. It may also be difficult to correct the tilted position of the bulb after mounting the lamp device on the external supporting device.